The present invention relates generally to the art of hydrolytic condensation polymers of organoalkoxysilanes, and also to the art of organic hybrid polymers of alkoxysilanes, and particularly to the art of coatings which attenuate ultraviolet radiation.
U.S. Pat. No. 4,405,679 to Fujioka et al. discloses a coated shaped article of a polycarbonate type resin of improved abrasion resistance comprising a shaped polycarbonate substrate, an undercoat applied and cured on the substrate, and an overcoat applied and cured on the undercoat comprising a hydrolyzate of an epoxy-containing silicon compound, at least one member of the group of hydrolyzates of organic silicon compounds, colloidal silica and organic titania compounds, and a curing catalyst.
U.S. Pat. Nos. 4,500,669 and 4,571,365 to Ashlock et al. disclose transparent, abrasion-resistant coating compositions comprising a colloidal dispersion of a water-insoluble dispersant in a water-alcohol solution of the partial condensate of silanol wherein the dispersant comprises metals, alloys, salts, oxides and hydroxides thereof.
In the Journal of Non-Crystalline Solids, Vol. 63 (1984), Philipp et al. disclose in xe2x80x9cNew Material for Contact Lenses Prepared From Si- and Ti-Alkoxides by the Sol-Gel Processxe2x80x9d that it is possible to combine inorganic and organic elements to develop materials with special properties.
To combine the mechanical strength and stability of inorganic materials with the flexibility and film-forming ability of organic materials is an objective of this invention. Organic-inorganic hybrid polymers in accordance with the present invention are prepared by hydrolytic condensation polymerization of an organoalkoxysilane in the presence of a water soluble organic polymer such as polyvinylpyrrolidone, preferably with an alkali metal carboxylic acid used as the condensation catalyst. Cerium oxide is preferably incorporated into the polymer for attenuation of ultraviolet radiation.
Commercial abrasion-resistant coatings for stretched acrylic either contain colloidal silica and exhibit poor resistance to corrosion by solvents such as acetone and sulfuric acid, or are based on relatively soft organic polymer systems such as urethanes or melamines.
The hydrolysis of silanes of the general formula RXSi(ORxe2x80x2)4-x, wherein R is an organic radical, Rxe2x80x2 is a hydrolyzable low molecular weight alkyl group and x is at least one and less than 4, such as methyltrimethoxysilane, dimethyldiethoxysilane and xcex1-methacryloxypropyltri-ethoxysilane can be carried out under controlled conditions in the presence of appropriate additives and produces stable, clear solutions that exhibit excellent adhesion to unprimed stretched or cast acrylic. Cured coatings, preferably about four microns thick, typically exhibit Bayer abrasion results (i.e., percent haze after 300 cycles of one kilogram load) of 5-10 percent, have a stress crazing time of 17 minutes upon exposure to acetone and 30 minutes upon exposure to 75% sulfuric acid under 3000 pounds per square inch pressure, and remain crack-free for up to 1900 hours of ultraviolet radiation exposure.